Coextrusion is a growing field of the extrusion art for products made with more than one material such as multilayered sheets or films. Coextrusion generally requires multiple extruders and specialized die systems to bring multiple layers together with a common sizing and shaping system. However, heretofore some material combinations have not been readily achieved in a melt combination die system due to wide differences in certain temperature dependent properties of the materials such as viscosity and degradation or die flow characteristics, so that other more time-consuming and/or expensive processes such as tandem extrusion have been utilized to form the material combination, but often with less than optimum results.
In particular, one area in which the need exists for an efficient and economical manner of combining materials having different temperature dependent properties is in the application of solventless or high solid, low-friction, abrasion-resistant polymer-based coatings to automotive weatherstrip and other product substrates for improving the performance and economic effectiveness of such products. More specifically, with regard to the differing temperature-dependent properties, selected polymer-based coatings have a processing temperature which is above the cure temperature of selected substrates, so that temperature isolation of the substrate and coating materials becomes necessary to avoid premature cure of the substrate during coextrusion of the materials. In addition, the performance and economic effectiveness of the final product is related to the thickness of the coating applied to the products, thus making the metering function of the apparatus and method of the present invention as important as the temperature isolation feature thereof which overcomes the differences in the temperature dependent properties of the coatings and product substrates.
Thus, the need exists for an apparatus and method for applying coatings to product substrates despite differences in the temperature dependent properties of the materials being combined, and further despite the need to meter one or more predetermined amounts of the coating onto one or more predetermined surfaces of the substrate.